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Trioctahedral Smectite and Interstratified Chlorite/Smectite in Jurassic Strata of the Connecticut Valley

Published online by Cambridge University Press:  01 July 2024

Richard H. April
Richard H. April*
Affiliation:
Department of Geology, Colgate University, Hamilton, New York 13346
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Abstract

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Trioctahedral smectite and regularly interstratified chlorite/smectite in strata of the East Berlin Formation of the Connecticut Valley are largely restricted to black shale and gray mudstone deposited in alkaline, perennial lakes. The precursor of the mixed-layer clay appears to have been a smectite. Alkaline lake waters and inherited pore waters rich in magnesium favored the transformation of smectite to mixed-layer chlorite/smectite by fixation of brucitic interlayers into the smectite unit structure. Gray mudstones containing the mixed-layer chlorite/smectite are invariably underlain by magnesium-rich black shale—a possible source of Mg for the clay mineral transformations. The black shale is composed predominantly of Mg-rich trioctahedral smectite of probable authigenic origin.

Резюме

Резюме

Триоктаэдрический смектит и регулярно внутринапластованный хлорит/смектит в пласте формации Восточного Берлина в Долине Коннектикута ограничены, в основном, до черной сланцеватой глины и серой иловатой глины, осажденных в щелочных непересыхающих озерах. Смектит кажется предшественником смешанно-слойной глины. Воды щелочных озер и наследственные пористые воды, богатые в магний, способствовали преобразованию смектита в смещаннослойный хлорит/смектит путем фиксации бруцитовых промежуточных слоев в элементарную структуру смектита. Черные сланцеватые глины, богатые в магний—возможные источники магния, используемые для преобразования глинистых минералов—неизменно располагаются под серыми иловатыми глинами, содержающими смешанно-слойный хлорит/смектит. Черная сланцеватая глина, в основном, состоит из богатого в магний триоктеэдрического смектита, вероятно, аутигенного начала. [Е.С.]

Resümee

Resümee

Trioktaedrischer Smektit und regelmäßge Chlorit/Smektit-Wechsellagerungen sind in den Schichten der East Berlin Formation des Connecticut Valley hauptsächlich auf schwarzen Schieferton und grauen Tonstein beschränkt, die in alkalischen permanenten Seen abgelagert sind. Der Vorläufer der Wechsellagerung scheint ein Smektit gewesen zu sein. Alkalische Seewässer und Mg-reiche Porenwässer begänstigten die Umwandlung des Smektit in die Chlorit/Smektit-Wechsellagerung, indem brucitische Zwischenlagen in die Smektit-Struktur eingebaut wurden. Unter den grauen Tonsteinen, die die Chlorit/Smektit-Wechsellagerung enthalten, findet sich immer ein Mg-reicher schwarzer Schieferton, der eine mögliche Mg-Quelle für die Tonmineralumbildung ist. Der schwarze Schieferton besteht vor allem aus Mgreichem trioktaedrischem Smektit mit wahrscheinlich authigener Entstehung. [U.W.]

Résumé

Résumé

La smectite trioctaèdre et la chlorite/smectite régulièrement interstratifiée dans les lits de la formation East Berlin de la vallée du Connecticut sont pour la plupart restrientes au shale noir et à l'argilite grise déposés dans des lacs alkalins perpétuels. Le précurseur de l'argile à couches mélangres semble avoir été une smectite. Les eaux alkalines du lac et les eaux héritées des pores, riches en magnésium, ont favorisé la transformation de la smectite en chlorite/smectite à couches mélangées par la fixation d'intercouches brucitiques dans la structure unitaire de la smectite. On trouve invariablement des shales noirs riches en magnésium, une source possible de Mg pour les transformations de minéral argileux, sous des argilites grises contenant la chlorite/smectite à couches mélangées. Le shale noir est composé surtout de smectite trioctaèdre riche en Mg et probablement d'origine authigénique. [D.J.]

Keywords

Alkaline lakeChloriteInterstratificationMagnesiumMudstoneShaleSmectite
Type
Research Article
Information
Clays and Clay Minerals , Volume 29 , Issue 1 , February 1981 , pp. 31 - 39
Copyright
Copyright © 1981, The Clay Minerals Society

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